Electrostencil

ABSTRACT

A STENCIL BLANK INCLUDES A STENCIL SHEET WHICH IS CAPABLE OF BEING PERFORATED BY ELECTRIC SPARKS, THE STENCIL SHEET BEING JUXTAPOSED WITH AND SUPPORTED ON A BACKING SHEET MADE OF AN ELECTRICALLY CONDUCTIVE MATERIAL. THE BACKING SHEET MAY COMPRISE ELECTRICALLY CONDUCTIVE BLACK GLAZED PAPER. THE STENCIL SHEET MAY BE FORMED ENTIRELY OF AN INHERENTLY ELECTRICALLY CONDUCTIVE SYNTHETI CRESIN. IN A MODIFIED FORM OF THE INVENTION, THE STENCIL SHEET COMPRISES A THIN SHEET OF PAPAER CONTAINING FINELY DISPERSED CARBON PARTICLES AND COATED WITH A LAYER OF INHERENTLY ELECTRICALLY CONDUCTIVE SYNTHETIC RESIN.

Feb. 9, 1971 I F H A 3,562,003

'-' ELEGTROS TENCIL Filed July 7, 1967 INVENTOR ALFRED FROHLICH UnitedStates Patent 3,562,003 ELECTROSTENCIL Alfred Frohlich, Hellerup,Denmark, assignor to Aktieselskabet for Kontor Kemi, Glostrup, Denmark,a corporation Filed July 7, 1967, Ser. No. 651,778

Claims priority, application Denmark, July 11, 1966,

Int. Cl. H01l1/06 US. Cl. 117--201 Claims ABSTRACT OF THE DISCLOSURE Astencil blank includes a stencil sheet which is capable of beingperforated by electric sparks, the stencil sheet being juxtaposed withand supported on a backing sheet made of an electrically conductivematerial. The backing sheet may comprise electrically conductive blackglazed paper. The stencil sheet may be formed entirely of an inherentlyelectrically conductive syntheti cresin. In a modified form of theinvention, the stencil sheet comprises a thin sheet of paper containingfinely dispersed carbon particles and coated with a layer of inherentlyelectrically conductive synthetic resin.

This invention relates to stencil blanks adapted to be electricallyperforated, and more specifically to stencil blanks of the typecomprising a stencil sheet having an electric conductivity suflicientfor perforation of the sheet by means of electric sparks, and a backingsheet.

Stencils of this type are known in various forms. The simplest inprinciple, however the most difficult to make, only consist of a backingsheet of paper of the type generally used for such purposes, and a filmof synthetic resin fastened thereto in a readily strippable manner, inwhich carbon particles, such as carbon black, are dispersed in such amanner that the carbon concentration and, accordingly, the electricconductivity of the film increases from the front side of the filmremote from the backing sheet towards the back side of the film.

Since the manufacture of thin sheets of synthetic resin having a carbonparticle concentration varying in a predetermined manner across thethickess of the film is exceedingly diflicult, it has also been proposedto compose the stencil sheet of a plurality of layers having differentcarbon particle concentrations. To this effect, the backing sheet may becoated first with a film of synthetic resin having a relatively highconcentration of carbon particles, and subsequently with an additioanlfilm having a lower carbon particle concentration. These films may beapplied in the form of solutions in different solvents. Alternatively, athin paper sheet loaded with carbon particles is coated on both sideswith synthetic resin equally containing carbon particles. The sheetprepared in this manner is fastened to the backing sheet in the mannerusual in stencil blanks.

A common drawback in the electro stencils described hereinbefore is thatthe manufacture thereof is complicated and expensive, because a veryhomogeneous, exactly proportioned distribution of the electricallyconductive particles over the area of the stencil sheet has to beinsured, and that, even if the stencil blank is made in the most carefulmanner, the prints made therewith become relatively unsharp and grainy,because the electric conductivity is limited to the several carbonparticles incorporated in the material.

In the case of electro stencils of resin-coated paper, a furtherinconvenience is that, when such stencils are used with duplicator inksof the emulsion type they have a very limited durability due to the factthat the resin coating, by reason of the carbon particles incorporatedtherein, is too porous to afford an effective protection of the paperagainst the water of the emulsoin type ink.

It is an object of this invention to remedy these disadvantages. To thiseffect, the invention provides a stencil blank of the kind referred to,in which at least a layer of the stencil sheet consists of an inherentlyelectrically conductive synthetic resin. Such resins may, in all of theknown electrostencils described hereinbefore, replace the carbonparticle loaded resins used heretofore, i.e. the stencil sheet mayconsist entirely of inherently electrically conductive synthetic reisn,or a thin sheet of paper loaded with carbon particles may be coated withsuch resin.

Synthetic resins having inherent electrically conductive properties areknown, but so far not in common use. Various groups thereof exists. Onegroup comprises polyolefins the chain structure of which has beenmodified through electronic bombardment. Another group comprisespolyamides made conductive through vacuum pyrolysis at 850 centigrade.Furthermore, various polymers are susceptible of transformation intopolykations connected with negative tetracyanoquino-di-methane ions, theconductivity being controlled by the amount oftetracyanoquino-di-methane used. This list is not complete, and aconstant development is taking place in this field.

The inherently electrically conductive synthetic resins afford theadvantage, as compared with the carbon particle loaded resins usedheretofore for electro stencils, that they are completely homogeneousand non-porous so that the electric conductivity is the same at allpoints. Accordingly, perforation through electric sparks may producestencil holes having sharp contours, however small they be. Furthermore,the resins in questions are waterproof so as to be well fit for use withduplicator inks of the emulsion type.

Reference will now be had to the accompanying drawings, in which:

FIG. 1 is an enlarged section view of one form of stencil blank inaccordance with this invention and FIG. 2 is a similar view of anotherform.

In the form shown in FIG. 1, a thin sheet 1 of a material such aspolyisobutylene which is made conductive through electronic bombardment,is fastened to a backing sheet 2 of electrically conductive paper, suchas black glazed paper, in such a manner as to be easily strippable fromthe backing. The electric conductivities of the stencil sheetconstituted by the polyisobutylene sheet and of the backing sheet,respectively, do not appear to be very critical, as long as theconductivity of the backing sheet is greater than that ofthe stencilsheet.

Instead of a backing sheet of electrically conductive paper, one ofusual paper having a conductive coating may, of course, be used, or thestencil sheet may be composed of two bonded resin layers havingdifferent conductivities.

According to FIG. 2, the stencil sheet 3 consists of a thin paper sheet4 having a weight of approximately 6- 12 grams per square meter andcontaining finely dispersed carbon particles, this sheet being coatedwith a thin film 5 of inherently electrically conductivepolyisobutylene. The backing sheet 6 may, as in FIG. 1, consist ofelectrically conductive paper, or may be provided with an electricallyconductive coating.

With this stencil, too, perforations having very sharp contours may beobtained, irrespective of the use of carbon particle loaded paper forthe stencil sheet.

The stencil blanks described may, if desired, be provided with anadditional coating of the stencil sheet for color contrast, in order tomake the perforations easily visible, such as is known in the art.

What I claim is:

1. A stencil blank comprising a stencil sheet capable of beingperforated by electric sparks, said sheet being juxtaposed with andfastened to a backing sheet of electrically conductive material, thestencil sheet comprising one or more layers at least one layer of thestencil sheet being formed a homogeneous inherently electricallyconductive synthetic resin, and the backing sheet being made of anelectrically conductive material.

2. A stencil blank as claimed in claim 1, wherein the stencil sheetconsists entirely of an inherently electrically conductive, syntheticresin.

3. A stencil blank as claimed in claim 2 wherein the backing sheetcomprises electrically conductive paper.

4. A stencil blank as claimed in claim 3 wherein the backing sheetcomprises black glazed paper.

5. A stencil blank as claimed in claim 1, wherein the r r v r l stencilsheet comprises a thin sheet of paper containing finely dispersed carbonparticles and coated with a layer of inherently electrically conductivesynthetic resin.

6. A stencil blank as claimed in claim 5 wherein the backing sheetcomprises electrically conductive paper.

7. A stencil blank as claimed in claim 6 wherein the backing sheetcomprises black glazed paper.

-8. A stencil blank as claimed in claim 1 wherein the conductivity ofthe backing sheet is gretaer than that of the stencil sheet.

9. A stencil blank as claimed in claim 1, wherein the backing sheetcomprises electrically conductive paper.

10. Astencil blank as claimed in claim 9, wherein the backing sheetcomprises black glazed paper.

References Cited UNITED STATES PATENTS 3,283,704 11/1966 Dalton 2072X3,376,810 4/1968 Blake et a1. 11735.5X 3,335,100 8/1967 Geyer 117-20lX3,424,698 1/1969 Lupinski et al 1l7201X WILLIAM L. JARVIS, PrimaryExaminer US. Cl. X.R.

